Background

Based on the monthly data of river runoff and major ion contents of the mainstream of the Yellow River during the period of 1956–2009, the effects of climate change on the trends of water quantity and major ion contents have been analyzed.

Results

The main conclusions have been drawn as follows: 1) The river runoff showed a significant decreasing trend from 1956 to 2009. 2) Total ion contents showed an increasing trend during this period, and there was a significantly negative correlation between the river runoff and total ion contents of the river. 3) There were two probable reasons for the increasing trends of major ion concentrations in the Yellow River. One was that the increasing of temperature caused by climate change enhances rock weathering; the other was that the decreasing trends of river runoff weaken its dilution effect for major ions in river water.

Conclusions

The results obtained in this research implicates that climate change will affect the major ion chemistry and water quality of the Yellow River. Further researches are needed to study the effects of climate change on water quality and water environment.

Due to the consumption of fossil fuels and other anthropogenic activities, the emission of greenhouse gases has increased, which have induced global climate change with warming as the significant feature (Jones et al.2009). Intergovernmental Panel Climate Change (IPCC) report points out that the earth’s surface temperature increased by 0.74°C during the last 100 years (1906–2005). Therefore, the global warming has been an indisputable fact at present Alley et al.2007). It may lead not only to a substantial temperature rising but also to a new pattern of surface water resources (Porcal et al.2009). The IPCC reports indicate that precipitation of some areas shows significant increasing trends, such as South America and east area in North America, while it exhibits the trend of droughts in the Mediterranean. From the above, we can easily draw the conclusion that climate change can influence the spatial distribution of water resources. Although the processes are uncertain, climate change is expected to produce drier summers and wetter winters across many places in the world (Arnell2004; Chaplot2007). In China, some researches have exhibited that climate change can impact the monthly variation of water quantity of rivers such as the Yellow River and the Heihe River (Hao et al.2006; Zhang et al.2007a; Qin et al.2010).

Not only water quantity but also water quality can be affected by climate change. There are also some evidences indicate that climate change can influence water quality worldwide (Wolfram & Heike2009; Burton et al.2010; Huang et al.2010). According to some research, the changes of precipitation, temperature, radiation, and wind caused by climate change will affect migration and transformation pathways as well as other biochemistry processes of pollutants in environment. It will lead to the change of reaction rate constant, adsorption rate, and dynamic constants of bioaccumulation of pollutants, resulting in the change of water quality (Frisk et al.1997; Yu et al.2002; Schiedek et al.2007; Elias & Elias2010). Therefore, climate change is an important factor affecting both water quantity and quality in rivers. Mimikou et al. (2000) have studied the effects of regional climate change on water quality in the Pinios river basin situated in the central part of Greece, and Prathumraana et al. (2008) have studied the lower Mekong River in Indochina; their results showed that the decrease of mean monthly runoff induced by climate change had led to the degradation of water quality. In addition, Jenet et al. (2010) have studied the impacts of regional climate change on water quality in the Murray-Darling Basin, Australia, and their results showed that regional climate changes, particularly increase in temperature and decrease in runoff volume, can also influence water quality. However, there are few research reports about the effect of climate change on water quality and quantity as well as the relationship between them of a river for a long period.

Therefore, this research took the Yellow River as an example to study the effect of climate change on water quantity and quality, especially the relationships between them. In detail, based on the monthly data of river runoff and major ion concentrations of the mainstream of the Yellow River during the period of 1956–2009, the effects of climate change on the trends of water quantity and major ion concentrations have been analyzed.

Introduction of the study area

The Yellow River is the second largest river in China which originates from the Tibetan Plateau, flows eastwards through the Loess Plateau and the North China Plain, inrushes into the Bohai Sea at Kenli County, Shandong Province, with the mainstream length of 5464 km and basin area of 752 000 km2. The river is divided into the upper, middle and lower reaches based on its geomorphology and climatic conditions. According to the Yellow River Water Resources Bulletin of 2008, the upper reaches are the section from the river source to Toudaoguai, where the climate is arid with an annual average precipitation of 396 mm. The middle reaches stretch from Toudaoguai to Huayuankou; this section is mainly located in the Loess Plateau with lots of tributaries. The climate is semiarid and arid with an annual average precipitation of 516 mm. The lower reaches stream down from Huayuankou; the climate is humid with an annual average precipitation of 648 mm.

The study on impacts of climate changes on the Yellow River basin is of great significance to the river management under climate change because of its growing economic and agricultural importance in China. Changes of water quality and quantity are of significance to water supply and demand in the Yellow River basin (Xia et al.2009a). Though there have been numerous studies about the water quantity and quality in the Yellow River (Xia et al.2009b; Yuan & Shu2008), few studies have been conducted on the effect of climate changes on the water quantity and quality of this river.

Data sources and methods

Three hydrological stations were studied in this research, which were the Lanzhou Station in the upper reaches, the Huayuankou Station in the middle reaches, and the Lijin Station in the lower reaches (Figure 1). Monthly water quality and quantity data of the three stations from 1956 to 2009 were retrieved from the Yellow River Conservancy Commission. Water quality parameters included Ca2+, Mg2+, K+, Na+, total ion concentrations, conductivity, pH and dissolved oxygen (DO). Water quantity data included river runoff. Based on the monthly data of river runoff and water quality parameters of the three stations from 1956 to 2009, the variation trends of the river runoff, major ion concentrations and other water quality parameters in the Yellow River were determined by chi-square test with SPSS 18.0 software (SPSS Inc., USA), and relationship between water quantity and water quality parameters of the Yellow River was studied by Pearson coefficient method.

The variation of water quantity

As shown in Figure 2, the annual natural runoff of the Yellow River showed a significant decreasing trend from 1956 to 2009 at the Lanzhou Station, Huayuankou Station and Lijin Station, and the decreasing extents were about 80 108 m3, 280 108 m3 and 300 108 m3 during the last 50 years, respectively. In addition, there was difference in river runoff trends among different seasons and different stations. For the Lanzhou Station, as shown in Figure 3, the river runoff exhibited an increasing trend in June, but decreased in wet seasons. At the same time, for the Huayuankou Station in the middle reaches and the Lijin Station in the lower reaches, the river runoff showed decreasing trends in each month, and the decreasing rates in wet season were higher than the other seasons.

Figure 2

The variation trend of annual natural runoff from 1956 to 2009.

Figure 3

The variation trend of river runoff at the Lanzhou Station in June and wet seasons (including July, August, September) from 1956 to 2000.

These results can be explained by changes of precipitation and temperature caused by climate change in the Yellow River basin. There have been findings about decrease of precipitation in the Yellow River basin during the past 50 years (Lan et al.2006; Zhang et al.2009). In addition, the annual mean temperature has increased 0.6°C in the Yellow River from 1950 to 2000 (Qiu et al.2003), especially after 2000, the mean annual temperature is 1°C higher than the 1950s (Yang et al.2009), and regional climate models predict that the temperature will increase by 3.44 ~3.90°C at the end of the 21st century (Yao et al.2009). The increase of temperature in the basin will lead to the increase of evaporation. Therefore, the decrease of precipitation and increase of evaporation have resulted in the decrease of river runoff of the Yellow River.

The variation of total ion contents and other water quality parameters

The concentrations of total ions, Ca2+, and Mg2+ in the Yellow River showed increasing trends from 1960 to 2000, especially obvious in wet seasons at the Lanzhou and Huayuankou stations (Figure 4). For the Huayuankou station, in addition to wet seasons, monthly averages of total ion concentrations, and Ca2+, Mg2+ concentrations in the other seasons increased from 1960 to 2000. And, electrical conductivity had strong relationship with total ion concentration at the Huayuakou Station; it also increased in wet seasons. Electrical conductivity represents the amount of total dissolved solids or total amount of dissolved ions in water. The increasing conductivity means higher dissolved ion concentrations in water (Kenneth et al.2005).

Figure 4

The variation trend of total ion contents at the Huayuankou Station.

pH was also analyzed as one of water quality parameters. From Figure 5, it’s obvious to find the decreasing trend of pH from 1992 to 2000. This was probably caused by the increasing emissions of acid rain precursors such as SO2 and NOx (Ji-Hyung et al.2010), which could be brought into the rivers through wet deposition. In addition, decreased water level could accelerate the oxidation process of sulfide of the riverbed. (Aherne et al.2006) and (Laudon2007) also obtained the similar results. (Aherne et al.2006) reported that recent recovery of surface waters from acidification has been delayed by drought induced SO42- export from wetlands in south-central Ontario, Canada. According to Laundon’s research (Laudon2007), recovery from episodic acidification was delayed by drought and high sea salt deposition in Sweden. In addition to that, (Evans et al.2007) found that frequent storms in the winter caused by climate change brought more acid ions such as SO42- to rivers, leading to the decrease of pH in a small, moorland stream in mid-Wales, UK.

Figure 5

Variation of annual pH value of river water at the Lanzhou Station and Huayuankou Station.

Another water quality parameter DO was also analyzed, but the variation trend was not obvious. This was probably because that DO content was not only influenced by temperature, river runoff, but also by conditions of water exchange and biological activities (Zhang et al.2007b); the organic matters transported from land to river by precipitation were assimilated by aerobic organisms using DO. Therefore, DO could not reflect the relationship between water quantity and water quality well. Prathumraana et al. (2008) also reported that DO had weak correlations with river runoff.

Relationship between water quantity and quality was analyzed based on the historical data of river runoff and total ion concentrations, Ca2+ and Mg2+ concentrations. Results in Table 1 and Figure 6 revealed the significant correlations between river runoff and water quality parameters of the Yellow River. Ion concentrations showed significantly negative correlation with river runoff, especially for the Huayuankou Station in August, September and October and for the Lanzhou Station in July. The results are similar to those obtained by (Wright & Worral2001), who reported that conductivity and a selection of metal ion concentrations such as Ca2+ and Mg2+ showed an inverse relationship with river flow in Tees estuary of the United Kingdom. It is suggested that Ca2+ and Mg2+ are mostly sourced from dissolution of rocks of the catchment; they enter river through base flow input. Higher river flow will dilute the concentration of these ions; on the contrary, lower runoff will increase the concentration of these ions (Chen et al.2002). The results obtained in this research indicated that major ion concentrations have response to the change of river runoff.

Table 1

Correlations of river runoff and major ion concentrations of the Yellow River at the Lanzhou and Huayuankou Station

Parameters

Runoff of Lanzhou station

Runoff of Huayuankou station

August

September

October

August

September

October

Ca2+ (Aug.)

-0.338*

-0.302

Ca2+ (Sep.)

-0.133

-0.237

Ca2+ (Oct.)

-0.007

-0.668**

Mg2+(Aug.)

-0.250

-0.324

Mg2+ (Sep.)

-5.44**

-0.447*

Mg2+ (Oct.)

-1.25

-0.597**

Total ions (Aug.)

-0.419*

-0.364

Total ions (Sep.)

-4.12*

-0.461*

Total ions (Oct.)

-0.074

-0.672**

*Correlation is significant at the 0.05 level.

**Correlation is significant at the 0.01 level.

Figure 6

Correlations between water quantity and total ion contents at the Lanzhou Station (p < 0.05) in July and at the Huayuankou Station (p < 0.05) in October.

Implications for the effect of climate change on the water quality and quantity of the Yellow River

There were two probable reasons for the increasing trends of major ion concentrations in the Yellow River. One was that the increasing of temperature caused by climate change enhances rock weathering, leading to the higher concentrations of major ions in river water. The other reason was that the decreasing trends of river runoff weaken its dilution effect for major ions in river water, resulting in the concentration of major ions. This was manifested by the negative correlation between river runoff and total ion concentrations. The decreasing trend of river runoff of the Yellow River and the increase of temperature were mainly caused by the climate change (Zeng et al.2004; Liu2007; Jia et al.2008). Therefore, the results obtained in this research implicates that climate change will affect the water quality including major ion concentrations, conductivity and pH value of rivers.

This research has shown the significant decreasing trend of water quantity and the increasing trend of major ion concentrations as well as the effects of climate change on both water quantity and quality of the Yellow River. Climate change has already produced a variety of unpredictable effects on water resources including water quantity and quality. Appropriate measures should be put forward to deal with climate change impacts, which can be used to mitigate the bad effects. Specific and practical options and positive ways to enhance adaptability to climate change should be proposed to decision-makers. To this end, the impact of climate change on water resources and water security should be studied, and further research are needed to study the effects of climate change on water quality and eco-environment of surface water.

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